Electric bicycles which are operated electromotively or in a hybrid operating state involving muscular power are referred to as “pedelecs” or “e-bikes”. Pedelecs and e-bikes differ in that, in pedelecs, the drive device has a mere supporting function and is effective depending on the torque applied by the cyclist riding the bicycle, whereas in e-bikes, the drive device is effective independently of the torque applied by the cyclist. The pedaling movement of the cyclist in pedelecs is therefore absolutely necessary for the drive device to be active.
A typical pedelec drive device is described DE 20 2014 103 462 U2. That drive device has a drive housing in which a bottom bracket shaft is rotatably supported, wherein a first pedal crank is arranged at one end of the bottom bracket shaft and a second crank pedal is arranged at the opposite end of the bottom bracket shaft, both pedals cranks being secured against rotation relative to the shaft. The bottom bracket shaft is connected to a hollow shaft via a cyclist's freewheel, the hollow shaft being arranged in the drive housing and being connected to a chain ring in a manner secured against rotation relative thereto. The hollow shaft is further directly connected to a pulley via a motor freewheel, the pulley being driven by an electric motor. The sum of the cyclist's torque and the torque generated by the drive device is transmitted to the rear wheel of the bicycle via the chain ring and a chain and, for example, a pinion cassette.
The assistance provided by the drive device depends on the torque generated by the cyclist during the pedaling movement and on an assistance level. The different assistance levels are typically predefined by the manufacturers of such drive devices. The torque generated by the cyclist during the pedaling movement is detected by a torque sensor that usually cooperates with the bottom bracket shaft and, for example, determines the torsion of the bottom bracket shaft and, from that, determines the cyclist's torque.
Such a design is disadvantageous in that only the magnitude of the cyclist's torque is determined; whether the cyclist's torque induced in the bottom bracket shaft by the first pedal crank and/or the second pedal crank is unknown.